U.S. patent application number 12/292009 was filed with the patent office on 2009-03-19 for method and apparatus for recycling inert gas.
This patent application is currently assigned to Rolls-Royce plc. Invention is credited to Jeffrey Allen, Justin M. Burrows, Daniel Clark.
Application Number | 20090071401 12/292009 |
Document ID | / |
Family ID | 33017359 |
Filed Date | 2009-03-19 |
United States Patent
Application |
20090071401 |
Kind Code |
A1 |
Clark; Daniel ; et
al. |
March 19, 2009 |
Method and apparatus for recycling inert gas
Abstract
A method for recycling an inert gas evacuated from a material
deposition process chamber 10 comprises cooling the evacuated inert
gas and recirculating a proportion of the cooled gas to the chamber
10 at a first temperature for use as a cooling gas in the material
deposition process 12, and recirculating a proportion of the cooled
gas to the chamber 10 at a second temperature for use as a
shielding gas in the material deposition process 12, the second
temperature being higher than the first temperature. Apparatus 22
for recycling an inert gas is also disclosed.
Inventors: |
Clark; Daniel; (Derby,
GB) ; Allen; Jeffrey; (Derby, GB) ; Burrows;
Justin M.; (Derby, GB) |
Correspondence
Address: |
MANELLI DENISON & SELTER
2000 M STREET NW SUITE 700
WASHINGTON
DC
20036-3307
US
|
Assignee: |
Rolls-Royce plc
|
Family ID: |
33017359 |
Appl. No.: |
12/292009 |
Filed: |
November 10, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11176305 |
Jul 8, 2005 |
7465476 |
|
|
12292009 |
|
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Current U.S.
Class: |
118/666 ;
118/61 |
Current CPC
Class: |
C23C 4/137 20160101;
B01D 2257/102 20130101; B01D 2257/104 20130101; C23C 8/00 20130101;
C23C 26/00 20130101; B01D 2257/80 20130101; B01D 2257/108
20130101 |
Class at
Publication: |
118/666 ;
118/61 |
International
Class: |
B05C 11/00 20060101
B05C011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 12, 2004 |
GB |
0417936.2 |
Claims
1-12. (canceled)
13. Apparatus for recycling an inert gas evacuated from a material
deposition process chamber, the apparatus comprising means for
cooling the evacuated inert gas to provide a cooled gas, means for
recirculating a proportion of the cooled gas to the chamber at a
first temperature for use as a cooling gas in the material
deposition process, and means for recirculating a proportion of the
cooled gas to the chamber at a second temperature for use as a
shielding gas in the material deposition process, the second
temperature being higher than the first temperature.
14. Apparatus according to claim 13, wherein the means for cooling
the evacuated inert gas comprises a gas cooler operable to cool the
evacuated gas to the first temperature.
15. Apparatus according to claim 14, wherein the means for
recirculating the cooled gas at the first temperature comprises a
pump device for recirculating the cooled gas directly from the gas
cooler to the chamber at the first temperature.
16. Apparatus according to claim 14, wherein the means for
recirculating the cooled gas at the second temperature comprises a
gas mixing device for mixing a proportion of the gas cooled to the
first temperature with a proportion of the uncooled evacuated gas
to raise the temperature of the gas to the second temperature,
prior to recirculation to the chamber.
17. Apparatus according to claim 13, wherein the apparatus further
comprise a gas scrubber, located between the chamber and the means
for cooling the evacuated gas, for removing impurities from the
evacuated gas.
18. Apparatus according to claim 13, wherein the apparatus
comprises means for directing the cooled gas at the first
temperature onto material deposited in the material deposition
process to cool the deposited material.
19. Apparatus according to claim 18, wherein the apparatus
comprises shielding means between the directing means and a heat
source used in the material deposition process.
20. Apparatus according to claim 13, wherein the apparatus
comprises a monitoring system for monitoring the first and second
temperatures, the monitoring system including a controller for
adjusting the recirculation rate to compensate for temperature
variations.
Description
[0001] The present invention relates to a method and apparatus for
recycling an inert gas evacuated from a material deposition process
chamber.
[0002] Material deposition processes, such as Shaped Metal
Deposition (SMD) and Direct Laser Deposition (DLD), are carried out
in an inert gas atmosphere to prevent oxidation of the deposited
material. Such processes are normally carried out in a chamber, for
example with a small internal over pressure, to which the inert gas
is supplied.
[0003] Conventionally, the inert gas is supplied to the chamber and
discarded after use such that a constant supply of the gas is
needed. This is inefficient, especially when inert gases having a
large specific heat capacity, such as helium, are used as these
tend to be expensive.
[0004] It would therefore be desirable to reduce the disadvantages
of the known process.
[0005] According to one aspect of the present invention, there is
provided a method for recycling an inert gas evacuated from a
material deposition process chamber, the method comprising:
[0006] after evacuation cooling the evacuated inert gas to provide
a cooled gas;
[0007] recirculating a proportion of the cooled gas to the chamber
at a first temperature for use as a cooling gas in the material
deposition process; and
[0008] recirculating a proportion of the cooled gas to the chamber
at a second temperature for use as a shielding gas in the material
deposition process, the second temperature being higher than the
first temperature.
[0009] According to another aspect of the present invention, there
is provided apparatus for recycling an inert gas evacuated from a
material deposition process chamber, the apparatus comprising means
for cooling the evacuated inert gas to provide a cooled gas, means
for recirculating a proportion of the cooled gas to the chamber at
a first temperature for use as a cooling gas in the material
deposition process, and means for recirculating a proportion of the
cooled gas to the chamber at a second temperature for use as a
shielding gas in the material deposition process, the second
temperature being higher than the first temperature.
[0010] Preferred features of the invention are defined in the
accompanying claims.
[0011] An embodiment of the invention will now be described by way
of example only and with reference to the accompanying drawings, in
which:--
[0012] FIG. 1 is a schematic view of a method and apparatus for
recycling inert gas according to the invention; and
[0013] FIG. 2 is a detailed view of the method and apparatus in use
with a material deposition process.
[0014] FIG. 1 illustrates diagrammatically a material deposition
process chamber 10 in which a material deposition process generally
designated with the reference numeral 12 is carried out. The
chamber 10 is in the form of a gas chamber to which an inert gas is
supplied. The chamber 10 is sealed to a high standard and gas is
supplied to the chamber 10 such that there is a small internal over
pressure. The chamber 10 contains a minimal amount of oxygen and
thus provides an inert gas atmosphere 14 in which the material
deposition process 12 can be carried out.
[0015] Referring to FIG. 2, one example of a material deposition
process 12 carried out in the chamber 10 is shown. The material
deposition process 12 is a conventional Shaped Metal Deposition
(SMD) process in which a heat source, for example a tungsten inert
gas (TIG) torch 16, is used to create an arc and melt a filler wire
18. When melted, the filler wire 18 is deposited onto an underlying
layer of material and solidifies to form deposited material 20. It
will of course be appreciated that the material deposition process
12 can be carried out using any suitable heat source, other than a
TIG torch 16, which requires an inert atmosphere. Techniques such
as laser and powder or wire deposition, low pressure electron beam,
etc, may alternatively be employed.
[0016] In order to optimise the properties of the deposited
material 20, it is necessary to control the temperature and cooling
rate at which the deposition process 12 is carried out. One method
by which temperature and cooling rate can be controlled is to use
an inert gas. The present invention provides apparatus 22 for
recycling the inert gas used in the material deposition process 12
which enables the gas temperature to be carefully controlled, as
will now be described.
[0017] Referring again to FIG. 1, the apparatus 22 comprises a
closed loop system for pumping inert gas from the chamber 10 and
recirculating it to the chamber 10. The apparatus 22 preferably
operates to continuously pump inert gas and recirculate it to the
chamber 10. The apparatus 22 comprises a first path 24 along which
gas is evacuated from the chamber 10 and supplied to a gas scrubber
26. The gas scrubber 26 is operable to purify the gas evacuated
from the chamber 10 by removing oxygen and moisture, and may remove
other gases such as nitrogen and hydrogen. Any suitable gas
scrubber 26 may be used, for example comprising a combination of
heaters and catalysts to cause the evacuated gas to react and
therefore to purify the gas.
[0018] A dehumidifier (not shown) may also be provided to remove
moisture from the evacuated inert gas.
[0019] Upon exit from the gas scrubber 26, a proportion of the
purified gas, which may for example be at a temperature in the
order of 20.degree. C., is supplied along a second path 28 to a
means for cooling the evacuated gas in the form of a gas cooler or
chiller 30. The gas cooler 30 is operable to cool the evacuated
inert gas to a first temperature which may for example be in the
order of -160.degree. C. Means in the form of a pump 32 is provided
for recirculating a proportion of the gas cooled to the first
temperature to the chamber 14. The gas is recirculated along a
thermally insulated gas pipe 34 and is supplied into the chamber 14
using a valve 36 which has a suitably low coefficient of thermal
expansion.
[0020] The cooled gas recirculated at the first temperature is used
as a cooling gas in the material deposition process 12 and in
particular enables the cooling rate of the deposited material 20 to
be carefully controlled. Referring to FIG. 2, according to one
embodiment of the invention, the apparatus 22 includes a gas lens
38, which may for example be a ceramic gas lens, for directing a
jet 40 of the gas cooled to the first temperature directly towards
the deposited material 20 to cool the deposited material 20.
Shielding means in the form of a shield or baffle 42 is mounted on
the end of the gas lens 38 and is positioned between the end of the
TIG torch 16 and the gas jet 40 to protect the arc formed by the
TIG torch 16 from turbulence formed by the jet 43 in the immediate
vicinity of the arc and also from the very low first temperature to
which the gas is cooled. Exposure of the arc to such a low
temperature may prevent proper melting of the filler wire 18 and
thus hinder material deposition.
[0021] The flow rate of the gas forming the gas jet 40 is variable
to enable the cooling rate of the deposited material 20 to be
carefully controlled. Although only one gas jet 40 is illustrated,
it is to be understood that any number of gas jets 40 may be
provided according to the particular application. In this case, the
flow rate of each gas jet 40 may be varied independently to control
the cooling rate of the deposited material 20.
[0022] When a plurality of gas jets 40 is provided, the temperature
of the gas supplied by each jet 40 may be independently variable
either as an alternative, or in addition, to the flow rate of the
gas. This further contributes to the ability to control the cooling
rate of the deposited material 20.
[0023] Referring again to FIG. 1, the apparatus 22 includes a gas
mixing device in the form of a gas mixer 42. A proportion of the
uncooled gas from the gas scrubber 26 is fed along a third path 44
to the gas mixer 42. Likewise, a proportion of the gas which has
been cooled to the first temperature in the gas cooler 30 is fed
along a fourth path 46 from the gas cooler 30 into the gas mixer
42. The uncooled gas from the scrubber 26 and the gas cooled to the
first temperature are mixed in the gas mixer 42 to thereby raise
the temperature of the cooled gas from the first temperature to a
second temperature, which is higher than the first temperature. For
example, the second temperature may be in the order of
15-20.degree. C.
[0024] Upon exit from the gas mixer 42, the gas at the second
temperature is recirculated into the chamber 10 along a fifth path
48. Most of the gas at the second temperature is supplied to the
TIG torch 16 where it acts as a shielding gas in the material
deposition process 12. A small proportion of the gas may also be
directed towards equipment, such as a camera 50, located in the
chamber 10 to cool the equipment and prevent damage thereto.
[0025] In an exemplary embodiment, the cooling gas cooled to the
first temperature may be recirculated to the chamber 10 along the
pipe 34 at a volume flow rate in the order of, for example, between
1000 and 2000 litres per minute, whilst the shielding gas at the
second temperature may be recirculated to the chamber 10 along the
fifth path 48 at a volume flow rate in the order of, for example,
between 15 and 100 litres per minute. It will however be
appreciated any suitable flow rates may be selected and will be
dependent upon the nature of the process, the required amount of
cooling of the evacuated gas, and the desired cooling rate of the
deposited material 20.
[0026] As mentioned, gas is supplied to the chamber 10 such that
there is a small internal over pressure, and this ensures that any
leaks which may occur between the chamber 10 and the outside
atmosphere are from the chamber 10 and not into the chamber 10. The
constant flow of gas around the closed loop system, and in
particular the evacuation of the gas from the chamber 10 along the
first path 24 via a constriction, ensures that a back pressure is
established inside the chamber thereby maintaining the chamber 10
at a positive pressure. In the illustrated embodiment, the gas is
evacuated from the chamber 10 through a constriction formed
directly in a side wall of the chamber 10. In another embodiment, a
side wall of the chamber 10 may include a plurality of perforations
over its entire area to thereby act as a reverse diffuser. This
would ensure an even flow of gas substantially across the whole
cross-section of the chamber 10. It would still be necessary to
provide a constriction before evacuating the gas along the first
path 24 to establish back pressure and thereby maintain the chamber
10 at a positive pressure.
[0027] In order to enable optimisation of the cooling of the
deposited material 20 and the deposition process shielding gas, the
apparatus 22 includes a temperature monitoring system (not shown).
The temperature monitoring system includes temperature sensors
which are operable to monitor at least the first and second
temperatures, and alternatively or in addition the temperature of
the deposited material 20 and the arc temperature of the material
deposition process 12. The temperature monitoring system includes a
controller which is operable to adjust the amount of cooling of the
evacuated gas, for example by varying the flow rate of evacuated
gas through the gas cooler 30, to thereby vary the first and/or
second temperatures. Additional means may also be provided to vary
the gas temperature.
[0028] The apparatus 20 may also include a pressure monitoring
system to enable the pressure within the chamber 10 to be carefully
monitored and controlled.
[0029] There is thus provided a method and apparatus 22 for
recycling an inert gas evacuated from a material deposition chamber
10. The method and apparatus ensures that the inert gas used in the
chamber 10 is continuously recycled and reused rather than being
discarded after use. Use of the apparatus 22 is therefore
particularly advantageous when the inert gas is an expensive gas,
such as helium. This is because at the large volume flow rates
required, it is uneconomic to use helium and discard the gas after
use. The method and apparatus 22 may however be used to recycle any
inert gas or any mixture of inert gases, for example a mixture of
argon and helium.
[0030] Although embodiments of the invention have been described in
the preceding paragraphs with reference to various examples, it
should be appreciated that various modifications to the examples
given may be made without departing from the scope of the present
invention, as claimed. For example, the apparatus may comprise at
least two gas coolers 30, one for cooling a proportion of the
evacuated gas to the first temperature and the other for cooling a
proportion of the evacuated gas to the second temperature. Under
these circumstances, the use of a gas mixer 42 may be
unnecessary.
* * * * *